Flask



FIG. 1 is a perspective view of a flask showing my new design;

FIG. 2 is a front elevational view, with the rear elevational view being identical thereto;

FIG. 3 is a side elevational view with the side opposite thereto being identical thereto;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof.

The broken line showing of the central region of the bottom surface is for environmental purposes only and forms no part of the claimed design. 

The ornamental design for a flask, as shown and described. 